It lies in the east of the country and is one of the federal states that was re-created in 1990 upon the reunification of the former West Germany and East Germany. Brandenburg surrounds but does not include the national capital and city-state Berlin.

Brandenburg is situated in territory known in antiquity as Magna Germania, which reached to the Vistula river. By the 7th century, Slavic peoples are believed to have settled in the Brandenburg area. The Slavs expanded from the east, possibly driven from their homelands in present-day Ukraine and perhaps Belarus by the invasions of the Huns and Avars. They relied heavily on river transport. The two principal Slavic groups in the present-day area of Brandenburg were the Hevelli in the west and the Sprevane in the east.

Beginning in the early 10th century, Henry the Fowler and his successors conquered territory up to the Oder River. Slavic settlements such as Brenna[3] (Brandenburg an der Havel), Budusin[4] (Bautzen), and Chośebuz[5] (Cottbus) came under imperial control through the installation of margraves. Their main function was to defend and protect the eastern marches. In 948 Emperor Otto I established margraves to exert imperial control over the pagan Slavs west of the Oder River. Otto founded the Bishoprics of Brandenburg and Havelberg. The Northern March was founded as a northeastern border territory of the Holy Roman Empire. However, a great uprising of Wends drove imperial forces from the territory of present-day Brandenburg in 983. The region returned to the control of Slavic leaders.

During the 12th century, the Ottonian German kings and emperors re-established control over the mixed Slav-inhabited lands of present-day Brandenburg, although some Slavs like the Sorbs in Lusatia adapted to Germanization while retaining their distinctiveness. The Roman Catholic Church brought bishoprics which, with their walled towns, afforded protection from attacks for the townspeople. With the monks and bishops, the history of the town of Brandenburg an der Havel, which was the first center of the state of Brandenburg, began. In 1134, in the wake of a German crusade against the Wends, the German magnate, Albert the Bear, was granted the Northern March by the Emperor Lothar III. He formally inherited the town of Brandenburg and the lands of the Hevelli from their last Wendish ruler, Pribislav, in 1150. After crushing a force of Sprevane who occupied the town of Brandenburg in the 1150s, Albert proclaimed himself ruler of the new Margraviate of Brandenburg. Albert, and his descendants the Ascanians, then made considerable progress in conquering, colonizing, Christianizing, and cultivating lands as far east as the Oder. Within this region, Slavic and German residents intermarried. During the 13th century, the Ascanians began acquiring territory east of the Oder, later known as the Neumark (see also Altmark).

In 1320, the Brandenburg Ascanian line came to an end, and from 1323 up until 1415 Brandenburg was under the control of the Wittelsbachs of Bavaria, followed by the Luxembourg Dynasties. Under the Luxembourgs, the Margrave of Brandenburg gained the status of a prince-elector of the Holy Roman Empire. In the years 1373-1415, Brandenburg has been a part of the Lands of the Bohemian Crown. In 1415, the Electorate of Brandenburg was granted by Emperor Sigismund to the House of Hohenzollern, which would rule until the end of World War I. The Hohenzollerns established their capital in Berlin, by then the economic center of Brandenburg.

When Frederick William died in 1688, he was followed by his son Frederick, third of that name in Brandenburg. As the lands that had been acquired in Prussia were outside the boundaries of the Holy Roman Empire, Frederick assumed (as Frederick I) the title of "King in Prussia" (1701). Although his self-promotion from margrave to king relied on his title to the Duchy of Prussia, Brandenburg was still the most important portion of the kingdom. However, this combined state is known as the Kingdom of Prussia.

Brandenburg remained the core of the Kingdom of Prussia, and it was the site of the kingdom's capitals, Berlin and Potsdam. When Prussia was subdivided into provinces in 1815, the territory of the Margraviate of Brandenburg became the Province of Brandenburg. In 1881, the City of Berlin was separated from the Province of Brandenburg. However, industrial towns ringing Berlin lay within Brandenburg, and the growth of the region's industrial economy brought an increase in the population of the province. The Province of Brandenburg had an area of 39,039 km2 (15,073 sq mi) and a population of 2.6 million (1925). After World War II, the Neumark, the part of Brandenburg east of the Oder-Neisse Line, was transferred to Poland; and its native German population expelled. The remainder of the province became a state in the Soviet Zone of occupation in Germany when Prussia was dissolved in 1947. Since the foundation of East Germany in 1949 Brandenburg formed one of its component states. The State of Brandenburg was completely dissolved in 1952 by the Socialist government of East Germany, doing away with all component states.

In 1952, the East German government divided Brandenburg among several Bezirke or districts. (See Administrative division of the German Democratic Republic). Most of Brandenburg lay within the Potsdam, Frankfurt (Oder), or Cottbus districts, but parts of the former province passed to the Schwerin, Neubrandenburg and Magdeburg districts (town Havelberg). East Germany relied heavily on lignite (the lowest grade of coal) as an energy source, and lignite strip mines marred areas of southeastern Brandenburg. The industrial towns surrounding Berlin were important to the East German economy, while rural Brandenburg remained mainly agricultural.

The present State of Brandenburg was re-established on 14 October 1990.[6] The newly elected Landtag of Brandenburg first met on 26 October 1990.[7] As in other former parts of East Germany, the lack of modern infrastructure and exposure to West Germany's competitive market economy brought widespread joblessness and economic difficulty. In the recent years, however, Brandenburg's infrastructure has been modernized and joblessness has slowly declined.

In 1995, the governments of Berlin and Brandenburg proposed to merge the states in order to form a new state with the name of "Berlin-Brandenburg", though some suggested calling the proposed new state "Prussia". The merger was rejected in a plebiscite in 1996 – while West Berliners voted for a merger, East Berliners and Brandenburgers voted against it.

The Oder River forms a part of the eastern border, the Elbe River a portion of the western border. The main rivers in the state itself are the Spree and the Havel. In the southeast, there is a wetlands region called the Spreewald; it is the northernmost part of Lusatia, where the Sorbs, a Slavic people, still live. These areas are bilingual, i.e., German and Sorbian are both used.

Brandenburg is known for its well-preserved natural environment and its ambitious natural protection policies which began in the 1990s. 15 large protected areas were designated following Germany's reunification. Each of them is provided with state-financed administration and a park ranger staff, who guide visitors and work to ensure nature conservation. Most protected areas have visitor centers.

^BP = Brandenburg Province, SB = Soviet Zone, Brandenburg. With the abolition of states in East Germany in 1952 vehicle registration followed the new Bezirk subdivisions. Since 1991 distinct prefixes are specified for each district.